This is how i run mine-
Fender '65 Deluxe Reverb Combo Re-issue
Line 6 POD XT Amp Modeler
Line 6 Shortboard (Foot controller thing)
Q Tron +
running to my Gibson Les Paul.
I think that the distortion models are very good, if you tweak them perfectly (some of them sound really awesome out of the box! some you have to tweak to your liking).
if you want the best distortion results, I'd go with a Fender tube amp through the Line 6 POD XT.
this is a really vague post by me, but your good either way. I mean, i use the POD XT moreso for effects than for the amp modeling (considering i have great tube amp), but every once in a while i'll put on a Marshall JST amp model on (i think its jst? can't remember). Anyways, just remember that the POD XT has a few Marshall models, probably all the ones you want. I'll look for a list of all the amp models.